JP2003209078A - Foam plastic sheet for polishing and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing pad in which clogging hardly occurs and the variation of polishing performance is reduced in the field of polishing, in particular, in a CMP process. <P>SOLUTION: A foam plastic sheet having long air bubbles arrayed in the same direction is manufactured as follows. As raw material plastic, a thermoplastic polyurethane elastomer (produced by DAINICHISEIKA Color and Chemicals MFG. Co,. Ltd.) is used and carbon dioxide and the raw material plastic are mixed in a first extruder. Resin pressure in a mixing zone is 25 MPa, a resin temperature is 200°C, and the carbon dioxide is in a supercritical state. The cross section of the sheet is observed along with an MD direction by an electron microscope. As a result, an average minor axis length is 24 μm, an average major axis length is 50 μm and an aspect ratio is 2.1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing sheet used for polishing semiconductors, substrates for various memory hard disks, etc., and a method for manufacturing the same, and in particular, semiconductor device wafers such as interlayer insulating films and metal wirings. The present invention relates to a polishing sheet which is preferably used for the surface flattening process and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a chemical mechanical polishing method (CMP) which is a typical process used for surface flattening of a semiconductor device wafer. For example, while dropping a polishing slurry, a semiconductor wafer is rotated and pressed against the surface of a polishing pad to flatten the surface of an object to be polished with high accuracy. Not only the polishing conditions, but also the characteristics of each component affect the flatness after polishing, the uniformity within the wafer surface, and the like. Among them, the polishing pad is one component that greatly affects the polishing performance,
The foaming state of the foamed sheet used as the polishing pad, that is, the bubble shape, the bubble diameter, and the like are important polishing factors.

Conventionally, in the CMP process, for example, an independent foaming type polishing pad (trade name: IC, using a thermosetting polyurethane manufactured by Rodel Co. as a matrix resin).
1000) and the like have been used as standard. According to the dressing before the polishing and the abrasion of the surface of the polishing pad with the progress of the polishing, the voids are opened and the retaining ability of the polishing slurry is developed. This type of polishing pad was apt to be clogged, and the polishing performance such as the polishing rate was likely to change or deteriorate with the increase in the number of polishing. The polishing pad must be replaced when the desired polishing performance is no longer obtained, but replacement of the pad is a task that requires a considerable amount of time even for a skilled worker, and this is one of the causes of lowering the throughput. The emergence of long pads has long been awaited.

Further, the partial polishing performance variation due to the density distribution in the polishing pad is one of the causes of the non-uniformity in the wafer surface. For example, in a lot having a wide density distribution, desired flatness cannot be obtained. There was a problem. Since this density distribution occurs not only in the polishing pad surface but also in the thickness direction, the conventional polishing pad has a possibility that variations in polishing performance may occur due to abrasion of the polishing pad itself as the polishing progresses. . Further, the conventional polishing pad in which the matrix resin forming the polishing pad is, for example, thermosetting polyurethane or the like requires a long time for the dressing process before use, which is also a cause of lowering the throughput.

With the recent remarkable development of the electronics industry, it has evolved into transistors, ICs, LSIs, and VLSIs. As the degree of integration of circuits in these semiconductor elements has rapidly increased, the design rules of semiconductor devices are becoming finer year by year. As the device becomes more and more popular, the depth of focus in the device manufacturing process has become shallower, and the flatness of the pattern formation surface has become more and more strict. Along with this, as the level of polishing performance required of polishing pads has increased, the problem of performance variation of conventional polishing pads has become apparent.

[0006]

DISCLOSURE OF THE INVENTION The present invention is to solve the problems of the conventional polishing pad, such as life and variations in polishing performance, and its object is to prevent clogging and to stabilize for a long time. Develops polishing performance,
An object of the present invention is to provide a plastic foam sheet for polishing having long cells arranged in the same direction and a method for manufacturing the same.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies in view of the problems of the prior art, and as a result, have accomplished the present invention by the following means. That is, the present invention is
(1) A plastic foam sheet for polishing characterized by having long cells arranged in the same direction, (2) a minor axis length of 1
The plastic foam sheet for polishing according to item (1), which has a size of at least μm and less than 60 μm, (3) a step of mixing the raw material plastic and a foaming agent, and a step of stretching the foam sheet to control the array direction and shape of the bubbles. The method for producing a plastic foam sheet for polishing according to (1) or (2), characterized in that (4) an inert gas as a foaming agent is mixed with the raw material plastic in a supercritical state. The method for producing a plastic foam sheet for polishing according to item (3).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The sheet in the present invention refers to all general films, sheets and boards. 2 and 3 show the plastic foam sheet for polishing of the present invention.
Will be explained. FIG. 2 is an example of a sheet cross section along the arrangement direction of long bubbles, and FIG. 3 is an example of a sheet cross section perpendicular to the arrangement direction of long bubbles. The long bubbles in the present invention,
The outer shape of the bubbles in the sheet cross section along the arrangement direction is an ellipse, and the average length of the minor axis per unit area (hereinafter,
The ratio of the average length of the long axis per unit area (hereinafter abbreviated as the long axis average length) to the short axis average length (hereinafter, abbreviated as the long axis average length), that is, the so-called aspect ratio is defined as bubbles.

Hereinafter, the description unless otherwise specified relates to the sheet cross section along the arrangement direction. In the plastic foam sheet for polishing of the present invention, during polishing, a flow occurs along the arrangement direction, so that the slurry is unlikely to stay on the polishing surface. Therefore, polishing dust is easily discharged and clogging is less likely to occur. As a result, stable polishing performance can be exhibited for a long time, and the life of the polishing pad is extended. The minor axis average length of the plastic foam sheet for polishing of the present invention is preferably 1 μm or more and less than 60 μm, more preferably 5 μm or more and less than 50 μm, and most preferably 10 μm or more and less than 40 μm. When it is 60 μm or more, the ability to retain the polishing slurry is significantly reduced and the polishing rate is reduced, which is not preferable. Conversely, if it is less than 1 μm,
Even long bubbles are not preferable because they tend to be clogged with polishing debris and the life is shortened.

The raw material plastic, which is one of the constituent materials of the foamed plastic sheet for polishing in the present invention, is not particularly limited, but thermoplastic elastomers such as polyurethane, polystyrene, polyester, polypropylene, nylon, polyvinyl chloride, polychlorinated. Vinylidene,
Polybutene, polyacetal, polyphenylene oxide, polyvinyl alcohol, polymethylmethacrylate, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polycarbonate, polyarylate, aromatic polysulfone resin, polyamide resin, polyimide resin, fluorine resin, Ethylene-propylene resin, ethylene-ethyl acrylate resin, acrylic resin, norbornene-based resin, styrene copolymer (for example, vinyl polyisoprene-styrene copolymer, butadiene-styrene copolymer, acrylonitrile-styrene copolymer, acrylonitrile- Butadiene
Styrene copolymer, etc.), natural rubber, synthetic rubber, etc. are preferable. These may be used alone, or may be mixed or copolymerized. Incidentally, from the viewpoint of a material having both suitability for foam molding and polishing performance, more preferably thermoplastic polyurethane elastomer, nylon, styrene copolymer, polymethylmethacrylate, fluororesin, polystyrene, polyester, polypropylene and the like, most preferably , A plastic obtained by mixing or copolymerizing these.

The step of mixing the raw material plastic of the present invention with the foaming agent is not particularly limited, but for example, an extruder is used to inject the foaming agent into the melt-kneaded raw material plastic.
The method of mixing is mentioned. The step of stretching the foamed sheet and controlling the cell array direction and shape is not particularly limited, but from the viewpoint of easiness of control, stability of product quality, economy, etc., for example, a steel belt, a roll or a combination thereof is used. There is a method.

The foaming agent of the present invention is not particularly limited. For example, all types of foaming agents can be used, including conventional chemical foaming agents and physical foaming agents. As the physical foaming agent, an inert gas for plastics such as argon, propane, butane, carbon dioxide and nitrogen is used alone or in combination of two or more kinds. These gases are usually
Since it has low compatibility with plastic and is difficult to mix, it is preferable to mix with plastic in a supercritical state. The supercritical state refers to a state at a critical temperature or a critical pressure or higher. For example, in the case of carbon dioxide, 7.3 M at 31 ° C. or higher.
Pa or higher. In the supercritical state, the viscosity is lower than that in the liquid state, the diffusion rate is faster, and the density is higher than that in the gas state, so that it can be dissolved in a large amount and quickly in the plastic, which is preferable.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the contents of the examples. <Formation of foamed sheet / polishing pad> In the center of the extruder,
The second extruder (barrel diameter 65 m) is attached to the first extruder (barrel diameter 50 mm) equipped with a nozzle for injecting a foaming agent.
m) is connected, and a lip width of 750 is provided at the tip of the second extruder.
A mm T-die was attached. The plastic sheet after exiting the T-die was stretched and cooled, processed into a sheet by trimming and cutting, and then punched into a disc having a diameter of 600 mm to prepare a polishing pad sample. Carbon dioxide was used as a foaming agent. The carbon dioxide taken out from the bomb was liquefied through a heat exchanger, then pressurized by a plunger pump and supplied through the nozzle in a fixed amount into the extruder.

<Evaluation of Polishing Performance> As an object to be polished, a 6-inch silicon wafer on which 10000 Å of Cu was formed by electrolytic plating was prepared. Polishing plate diameter 600m
m single-side polishing machine was used. A polishing pad is attached to the surface plate of the polishing machine with a double-sided tape, first, while the ion-exchanged water is dropped, the polishing pad surface is dressed with a diamond disk, and then a polishing slurry manufactured by Cabot (trade name: iCue5003) is poured. While 1 minute,
The Cu film was polished.

As the polishing conditions, the load applied to the wafer is 350 g / cm ² , the rotation number of the surface plate is 70 rpm, the rotation number of the wafer is 70 rpm, and the flow rate of the polishing slurry is 200 ml.
/ Min. After cleaning and drying the wafer after polishing, the Cu film thickness was measured at 49 points on the wafer surface using a 4-probe sheet resistance measuring machine, and flatness and in-plane uniformity were used as an index of polishing performance. Compared with. Further, the state of clogging of the polishing pad surface after polishing was observed using an electron microscope.

Example 1 A thermoplastic polyurethane elastomer (manufactured by Dainichiseika) was used as a raw material plastic. Carbon dioxide and raw plastic were mixed in the first extruder. The resin pressure in the mixing zone was 25 MPa, the resin temperature was 200 ° C., and carbon dioxide was in the supercritical state. In addition, as a result of observing a sheet cross section using a steel belt for stretching and cooling of the plastic sheet after exiting the T-die with an electron microscope along the MD direction, the short-axis average length was 24 μm, and the long-axis average length was 24 μm. Is 50μ
m, the aspect ratio was 2.1.

(Example 2) A sheet was formed into a sheet under the same conditions as in Example 1 except that the steel belt was changed to three rolls, and the cross section of the sheet was observed with an electron microscope. As a result, the short axis average length was 31 μm. The major axis average length was 68 μm, and the aspect ratio was 2.2.

Example 3 As a raw material plastic, a blend of a thermoplastic polyurethane elastomer (manufactured by Dainichiseika) and polystyrene (manufactured by A & M Styrene) was used. Carbon dioxide and raw plastic were mixed in the first extruder. The resin pressure in the mixing zone was 26 MPa, the resin temperature was 210 ° C., and carbon dioxide was in the supercritical state. In addition, as a result of observing a sheet cross section using a steel belt for stretching and cooling of the plastic sheet after exiting the T die with an electron microscope along the MD direction, the short axis average length was 19 μm, and the long axis average length was 19 μm. It is 51μ
m, and the aspect ratio was 2.7.

(Comparative Example 1) Sheets were formed under the same conditions as in (Example 1) except that the stretching speed was adjusted, and the short axis average length was 2
A foamed sheet having a size of 8 μm, a long axis average length of 32 μm and an aspect ratio of 1.1 was obtained. (Comparative Example 2) As a polishing pad, IC1000 (manufactured by Rodel) was used.

<Evaluation Results> (Example 1) to (Example 3)
In comparison with (Comparative Example 1) and (Comparative Example 2),
The in-plane uniformity was good. Further, at the stage of polishing about 80 Cu-formed wafers in (Comparative Example 1) and at the stage of polishing about 100 in (Comparative Example 2), partial clogging starts to be observed on the polishing pad surface. At the same time, both the polishing rate and the in-plane uniformity started to decrease, but in (Example 1) to (Example 3), no clogging was observed even after polishing about 100 sheets, and the polishing rate and in-plane uniformity There was no decrease in sex. In addition, the time required for the dressing of (Example 1) to (Example 3) was half or less that of (Comparative Example 2).

[0021]

EFFECT OF THE INVENTION By using the plastic foam sheet for polishing having long bubbles of the present invention for a polishing pad, clogging, variation in polishing performance and the like, which have been problems in the past, can be improved. As a result, stable polishing performance can be obtained for a longer time than in the conventional case, the frequency of pad replacement can be reduced, and throughput in the polishing process is improved.
In addition, in a supercritical state, an inert gas, which is a foaming agent, is mixed with raw material plastic to form a sheet,
By controlling the array direction and shape of the bubbles by stretching, the plastic foam sheet for polishing can be stably manufactured with good productivity.

[Brief description of drawings]

FIG. 1 is an example of a standard process of chemical mechanical polishing (CMP).

FIG. 2 is an example of a sheet cross section along the arrangement direction of long bubbles according to the present invention.

FIG. 3 is an example of a sheet cross section perpendicular to the arrangement direction of long bubbles according to the present invention.

[Explanation of symbols]

1 Semiconductor wafer 2 surface plate 3 dressing discs 4 Polishing slurry 5 Sample holder 6 polishing pad 7 rotation axis 8 Wafer fixing jig 9 Dressing disc holder 10 Slurry supply pipe 11 long bubbles

Claims (4)

[Claims] 1. A plastic foam sheet for polishing, which has long cells arranged in the same direction. 2. The plastic foam sheet for polishing according to claim 1, wherein the short axis average length is 1 μm or more and less than 60 μm. 3. The polishing plastic according to claim 1, further comprising a step of mixing the raw material plastic and a foaming agent and a step of stretching the foamed sheet to control the array direction and shape of the bubbles. Foam sheet manufacturing method 4. An inert gas as a foaming agent is mixed with a raw material plastic in a supercritical state,
The method for producing the plastic foam sheet for polishing according to claim 3.